Anode for cathodic protection systems



Feb. 20, 1962 5 P. ANDERSON 3,022,242

ANODE FOR CATHODIC PROTECTION SYSTEMS Filed Jan. 23, 1959 Wafer A e/ue/ INVENTOR.

EDWARD P. ANDERSON 7M (5: 73V 04. I

ATTORNEYS United Slates Patent This invention relates to an anode for cathodic protection systems or for similar applications in which a liquid forms part of an electric circuit.

Up to the present time cathodic protection has been employed primarily to avoid rusting or electrolytic corrosion of boats or other structures having large smooth surfaces which are exposed to salt water. For these purposes anodes which are evenly spaced with respect to the surface to be protected may be employed. A voltage of the proper level is applied between the anodes and the surface and a protective current flows from the anodes through the water to the ship or other structure to be protected. In these arrangements it'is particularly desirable that a fairly uniform current distribution be present over the entire surface to be protected.

It would also be desirable to employ cathodic protection for irregularly shaped metallic structures such as bridges, docks or canal gates, for example. In the case of these irregularly shaped structures it is difiicult to obtain the proper uniform current distribution over the surface to be protected.

Accordingly, an important object of the present invention is the elimination of corrosion on irregularly shaped structures through the use of a suitable cathodic protection system.

This object may advantageously be achieved through the use of an anode made of an elongated conductor covered with a layer of insulating material, the layer having a multitude of perforations or openings therethrough. Preferably, a wire serves as the conductor, and good results have been obtained using platinum-plated titanium wires. When used in connection with the cathodic protection of large underwater structures such as chains, cables, or the lattice-work of bridge supports consisting of steel beams, the anode wires according to the invention are wound helically around the structure or structural element to be protected, whereby the insulating layer prevents a short circuit from the wire core to the structure.- Electrical contact between the water and the wire occurs through the perforations in the insulating layer. The insulating material must be resistant to the electrolytic decomposition products of the water in which the structure is submerged. By way of example, suitable insulating layers have been formed of fiber glass reinforced polyesters such as polytetrafluoroethylene or polytrifluorochloroethylene.

In order to prevent direct contact between the anode wire and the irregular metallic structure through the openings in the insulating material, it is desirable that the insulating coating be relatively thick and that the openings be relatively small, with respect to the surface irregularities of the metallic structure to be protected. More specifically, in order to avoid grounding between the wire anode and the metallic structure, the ratio of the thickness of the insulating material to the largest dimension of the openings should be greater than the ratio of the depth to the cross section of projecting portions of the irregular structure in contact with openings in the insulating material.

The invention will be further illustrated by reference to the accompanying drawing in which:

FIGURE 1 is an isometric, fragmentary view of an anode according to the invention,

3,022,242 Patented Feb. 20, 1962 FIGURE. 2 is an elevational view of a lattice structure'having an anode mounted thereon, and

FIGURE 3 is a longitudinal section through an insulator suitable for spacing the anode from the structure to be protected.

Referring to FIGURE 1, the anode according to the invention consists basically of .a titanium wire 10 provided with a coating 12 of platinum, which may be applied by electroplating. The plated wire is covered by a layer 14 of insulatingmaterial having a multitude of perforations 16 therethrough. While satisfactory results have been obtained when insulating the anode wire by a layer of polytetrafluoroethylene, any other suitable insulating material, which is sufiiciently resistant tochemical attack by the decomposition products of the water surrounding the anode wire, can be used. The perforations 16'may be'readily formed, for example, by machine cutting the insulating layer on the wire which has first been fabricated witha continuous insulation covering. Other techniques for forming or depositing a perforate layer of insulation on a wire may be readily devised by one skilled in the art. As a result, -a lattice-like structure 14 of an insulating coating is provided which prevents electrical contact between the platinum surface 12 and the structure to be protected. Instead of a wire, tapes or elongated conductors having other shapes may be employed.

The wire shaped anodes are readily mounted near the structure to be protected. Advantageously this may be accomplished by winding the wire anodes 18 helically around beams, a chain, a cable or the elements 20 of a lattice structure, as shown in FIGURE 2. By interlacing the wire anode through the structure, equal current distribution over all surface elements may be obtained.

In order to prevent the possibility of mechanical stress tending to damage the insulation 14 at points of strong pressure against the adjacent structure, the invention provides spacing members in the form of stand-off insulators 22 as shown in FIGURE 3, which may be mounted at intervals on the wire anode 18. Made preferably from an insulating material, for instance, a fiber glass reinforced polyester, each cylindrical insulator 22 is provided with an axial bore 24 which forms a passageway for the wire anode 18. In order to maintain the insulator 22 in its position with respect to the wire anode, compression wire stops may be mounted adjacent the sides 26 and 28 of the insulator 22. Each compression wire stop, operating in a manner similar to that of a stuffing box, comprises a gland 30 having an internal thread which cooperates with a jam nut 32 to compress a packing 34. However, any other suitable means to maintain the insulating distancing members 22 at the desired intervals can be used. As an example, two insulators 36 and 38 are shown in FIGURE 2.

In FIGURE 2, a power supply 40 is connected between the framework 20 and the anode wire 18 at a point above the water level. The nature of suitable power supply requirements is well known in the art and one representative system is set forth, for example in co-pending application Serial No. 732,275, filed May 1, 1958.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. In a cathodic protection system, an elongated corrosion-resistant bare conductor serving as the anode, a metal object to be protected, means including an insulating layer having a large number of openings therethrough and covering said conductor for avoiding mechanical contact of said conductor with said metal object, while permitting fluid flow to the surface of said conductor, said conductor being wound around said object, and means for applying protective current between said conductor and saidobject: U

2. In a cathodic protection system, a wire having a corrosion-resistant metal surface, a perforated insulating layer covering; said wire, said layer forming distinct bare areas of the conductor surfacefor direct contact with a surrounding fluid, a-metalstnicture to be protected; said wirebeing' wound around the structure, and means for I slayer arrangedwrappedaround the submerged surface of said structure and means for applying directprotective applying direct protective current between said wire and said metal'stru'cture; r t

' It. In a cathodic protection system, a metal'ob ject 'to a current between said conductor and said structure. I

5. In a cathodic protection system, a metallic lattice structure to be protected and at least partly submerged in water, a bareplatinumecoated titaniurniwire vserving as the anode and covered witlra perforated insulating layer interlaced with the immersedportion, of said. lattice structure, and means: forapplying directprotective current between said: wire and said, structure. U

References Citedlin the of this patent UNITED STATES PATENTS a. OTHER REFERENCES 'Cotton-z "Pl'atinuim Metals Review, vol. '2, No. 2, April 1958, published by "Johnson, Matthey & Co. Ltd., London' V I 

1. IN A CATHODIC PROTECTION SYSTEM, AN ELONGATED CORROSIN-RESISTANT BARE CONDUCTOR SERVING AS THE ANODE, A METAL OBJECT TO BE PROTECTED, MEANS INCLUDING AN INSULATING LAYER HAVING A LARGE NUMBER OF OPENINGS THERETHROUGH AND COVERING SAID CONDUCTOR FOR AVOIDING MECHANICAL CONTACT OF SAID CONDUCTOR WITH SAID METAL OBJECT, WHILE PERMITTING FLUID FLOW TO THE SURFACE OF SAID CONDUCTOR, SAID CONDUCTOR BEING WOUND AROUND SAID OBJECT, AND MEANS FOR APPLYING DIRECT PROTECTIVE CURRENT BETWEEN SAID CONDUCTOR AND SAID OBJECT. 